Segment Reporting (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Gross inpatient revenues		$ 8,612,904	$ 7,680,132	$ 17,376,928	$ 15,460,984
Gross outpatient revenues		4,027,863	3,544,242	7,997,705	7,084,879
Total net revenues		2,681,353	2,612,356	5,368,869	5,225,214
Income/(loss) before allocation of corporate overhead and income taxes		301,770	294,271	598,008	612,697
Allocation of corporate overhead		0	0	0	0
Income/(loss) after allocation of corporate overhead and before income taxes		301,770	294,271	598,008	612,697
Total assets		11,069,417	10,552,487	11,069,417	10,552,487	$ 10,761,828
Acute Care Hospital Services
Segment Reporting Information [Line Items]
Gross inpatient revenues		6,164,010	5,430,997	12,525,776	11,028,847
Gross outpatient revenues		3,760,326	3,286,930	7,474,987	6,581,107
Total net revenues		1,403,991	1,366,457	2,849,623	2,756,004
Income/(loss) before allocation of corporate overhead and income taxes		162,015	157,877	365,726	345,681
Allocation of corporate overhead		(49,902)	(45,675)	(99,793)	(91,351)
Income/(loss) after allocation of corporate overhead and before income taxes		112,113	112,202	265,933	254,330
Total assets		3,971,106	3,754,983	3,971,106	3,754,983
Behavioral Health Services
Segment Reporting Information [Line Items]
Gross inpatient revenues	[1]	2,448,894	2,249,135	4,851,152	4,432,137
Gross outpatient revenues	[1]	267,537	257,312	522,718	503,772
Total net revenues	[1]	1,274,083	1,242,561	2,512,079	2,460,683
Income/(loss) before allocation of corporate overhead and income taxes	[1]	261,444	252,146	500,192	504,077
Allocation of corporate overhead	[1]	(40,246)	(39,653)	(80,578)	(79,314)
Income/(loss) after allocation of corporate overhead and before income taxes	[1]	221,198	212,493	419,614	424,763
Total assets	[1]	6,746,272	6,541,328	6,746,272	6,541,328
Other
Segment Reporting Information [Line Items]
Gross inpatient revenues		0	0	0	0
Gross outpatient revenues		0	0	0	0
Total net revenues		3,279	3,338	7,167	8,527
Income/(loss) before allocation of corporate overhead and income taxes		(121,689)	(115,752)	(267,910)	(237,061)
Allocation of corporate overhead		90,148	85,328	180,371	170,665
Income/(loss) after allocation of corporate overhead and before income taxes		(31,541)	(30,424)	(87,539)	(66,396)
Total assets		$ 352,039	$ 256,176	$ 352,039	$ 256,176

[1] Includes net revenues generated from our behavioral health care facilities located in the U.K. amounting to approximately $119 million and $106 million for the three-month periods ended June 30, 2018 and 2017, respectively, and approximately $234 million and $206 million for the six-month periods ended June 30, 2018 and 2017 respectively. Total assets at our U.K. behavioral health care facilities were approximately $1.123 billion and $1.028 billion as of June 30, 2018 and 2017, respectively.